Aquinas' main argument is well known as 'Aquinas' third way'; the argument from contingency and necessity. The first of Aquinas' ways was 'from motion,' this follows the idea that all objects move and a change of quality is movement. Nothing can move itself, which then leads to the idea of a chain of movement but the chain cannot be infinate, therfor there must be an unmoved mover to begin the chain. This first mover is God. The second of Aquinas' ways was 'from efficiant causes,' this follows the idea that all things are caused by something else because they cant cause themselves or they would exist before themselves.
However this would mean that there cant be an infinite chain of causes, meaning there must be a 1st cause that caused all causes, then this 1st cause is God. The third of Aquinas' ways is 'from contingency and necessity. This follows the idea that everything is dependant of factors outside itself, therefor everything is contingent. If this is correct then there must be a necessary being upon which everything is dependant on. The necessary being is God.
Another part to the cosmological argument is the Kalam argument which was developed by Al Ghazali and recently developed by Craig. The Kalam argument rejects the idea of an actual infinite because an actual infinite past of the universe is impossible. Craig developed the Kalam argument and added that it is logically unsound to propose an infinite series because for this to actually occur we would have to have travelled an infinite length of time and so still wouldnt be in the present yet.
However, some would critique Aquinas’ theory, for example; Hick pokes holes in aquinas's ‘three ways. ’ Hick says that Aquinas present us with two alternatives; that the universe is either “a fact”, or there is a ‘first cause’. Aquinas' argument can only be proven if there is evidence of a first cause of the universe. (ii )Consider the view that the strengths are more convincing than the weaknesses (9) Leibniz argued that there had to be a sufficient reason for the universe to exist which supports Aquinas's theory.
Leibniz says that even if the universe had always been in existence, it would still require an explanation for its existence so we can establish that there is something rather than nothing. Since there is nothing within the universe to show why it exists the reason must therefor exist outside of it. However Hume disagrees with Aquinas and observes that to arrive at the existance of god from the premises of the cosmological argument, this requires an inductive leap which ineffectively guesses without having actual evidence that allows for the assumption to be made.
This then means that you cannot make an inductive leap about the universe because we cannot make conclusions about something outside our exerience. In contrast to Hume copelston suports Aquinas' rejection of infinite regress based on the idea that an infinite chain of contingent beings would only consist of contingent beings therefor meaning they could never be able to bring themselves into existence. However like Hume, Mackie disagrees with Aquinas' inductive leap by stating hat ' everything at some time must exist' to 'at some point sometime everything does not exist' here there is a clear overlap of things that just dont make sense to put after eachother as there is clearly something missing in the middle. Taking these points into consideration we can make the assumption that the weaknesses are in actual fact stronger than the strengths because the strenghts agree with the inductive leap aquinas has made, however the leap clearly looks as if something in the middle is missing as you just cant make an assumption on something bigger than us that we have no expience of.